Radiation counter tube



Aug. 2, 1955 N. WARMOLTZ ET AL RADIATION COUNTEIR TUBE Filed June 13 1951 INVENTORS NICOLAAS WARMOLTZ GERHART WOLFGANG RAT %%HENAU United States Patent O 2714,680 RADIATION COUNTER TUBE Nicolaas Warmoltz and Gerhart Wolfgang Rathenau, Eindhoven, N etherlands, assignors to Hartford National Bank and Trost Company, Hartford, Conn. as trustee Application June 13, 1951, Serial N0. 231,302 Claims priority, application Netherlands Inne 23, 1950 6 Claims. (C1. 313-93) radiation counter tubes, the a constituent which acts to This invention relates to gas-filling of which contains quench the dis'charge.

This constituent exercises a great influence on the characteristic curve of the tube, especially in the interval within which, in the case of variation of the voltage the sensitivity of the counter tube does not substantially vary which interval will be referred to hereinafter as the lateau. The wider and flatter this lateau, the better. A plateau width of 200 volts and a variation of sensitivity over this interval of not more than some few percent per 100 volts is to be looked upon as favourable.

Satisfaetory results in this respect can be obtained With the use of definite hydrocarbon compounds and also With the use of halogens. However, eounter tubes containing such gases have the disadvantage that their characteristic curve is in time adversely afiected. With tubes having a hydrocarbon coxnpound this is due to dissociation of this cornpound by the electric dis'charge and With tubes containing halogen it is due to chemical reaction of the quenching gas With the metal of which the electrodes are made, With the result that the quenching gas is absorbed.

The influence of this absorption can be reduced by previously causing the parts by which the tube is constituted to remain fr some time in an atmosphere of the quenching gas to be used so that these arts are, as it were, saturated With this gas. However, this method has the diS* advantage that when the temperature of the tube increases, halogen is released, With the result that the slope and width of the plateau vary. Thus, for example, in a tube the electrodes of which were saturated With bromine, the operating voltage (lower limit of the lateau) was consequently displaced frorn 275 to 360 volts.

The invention enables halogen to be used as a quenching gas, the above-mentioned disadvantages being mitigated.

According to the invention, a radiation counter tube gas and an admixture of halogen is characterized in that the total or a considerable part of the total surface area of the metal parts of the tube in contact With said mixture is made of chromium sesquioxide.

Chromium sesquioxide reacts With the halogen to a limited extent such that the decrease of the amount of quenching gas is sufliciently slow. The characteristic curve of a counter tube according to the invention is substantially constant. Since there is no necessity for allowing for the absorption of the halogen, the percentage of halogen may be chosen according to the desired operating voltage.

If a Single metal part which constitutes a small part of the total surface area in contact With the gas mixture or a small part of a further metal part is not provided With a chromium sesquioxide surface, the quality of the tube is not adversely affected. Thus, for exarnple, it is not necessary to provide the anode With a chromium sesqui oxide surface if it is constituted by a metal wire or a thin rod arranged coaxially With a cylindrical cathode. In contradistinction thereto, it is suitable to give the cathode containing an ionisable 2,714,680 Patented Aug. 2, 1955 a surface of chromium sesquioxide, sinne it constitutes a considerable part of the total surface area of the metal parts in contact With the gaseous mixture. Also in the case of other metal parts having surface area, for example, the artition sometimes contained in radiation counter tubes, the provision of a chro mium sesquioxide surface aifords an important improvement.

The above-mentioned disadvantages of the halogens were particularly apparent With chlorine. For this reason, the use of halogen as an extinction gas was limited in practice to bromine although chlorine yields better results as far as the electrical properties of the tube are concerned. With the use of the invention, the improved results due to the use of chlorine may be obtained.

Chlorine has the additional advantage of rendering the tube suitable for a wider temperature range. Its vapour pressure rernains still high enough when the temperature falls below the value at which the vapour pressure of bromine becornes insuffieient for satisfactory operation.

A counter tube according to the invention may contain, for exarnple, a gas mixture under a pressure of 10 millimetres of mercury which is constituted primarily by neon and/or argon and for a small part by some tenths of a percent of ehlorine or bromine.

In order that the invention may be more clearly Underand readily carried into effect, scnbed more fully With reference to the accornpanying diagrammatic drawing, given by way of example, showing one embodirnent of a munter tube according to the invention.

Referring now to the figure, a cathode 1, which is shaped in the forrn of a hollow cylinder and which forms part cf the outer wall of a radiation munter tube is pro vided on 1e inner surface With a continuous protective layer 2 of chrornium sesquioxide. A rod-like anode 3, which is arranged coaxially With the cathode may also be provided With a chromium sesquioxide szurface but this is of little importance, because it has a very small surface area compared With the cathode. The layer of chromium sesquioxide keeps the metal by which the coated electrode is otherwise constituted (for example copper) from contact With the gas With which the tube is filled.

The electrodes may alternatively be made of an alloy containing chromiurn. If the chrornium is alloyed With one or more metals which oxiclise at a higher oxygen pressure than chrornium, a protective layer may be obtained by preferential oxidation. In this process, the conditions 0f oxidation will be such that the chromium alone oxidis'es, to chromiurn sesquioxide, and the other component or cornponents of the alloy do not. An ailoy suitable in this respect is constitnted rnainly by iron and chromium in a weight ratio of 1:0.25 t0 40. Such an alloy has the additional advantage that the glass sealing rnember 4 can readily be sealed hermetically to the electrodes.

As an alternative, the electrodes may first be chromiutnplated and at least the surf ce of the chromium layer may then be oxidised to chrornium sesquioxide.

The desirecl extent of oxidation depends on the gas used. If the extinction gas is t0 be consiituted by chlorine, more care should be taken than when it is to be constituted by bromine.

Bromine gas requires more complete oxidation than iodine gas which, however, is not so suitable as a quenching gas as brornine.

The window 5 through which the radiation to be examined enters the tube may be formed by mica. lt is seeured hermetically to the cylinder 2 by means of a ring 6 formed by melting of pulverulent glass.

What we clairn is:

l. A radiation counter tube comprising an envelope, a pair of electrodes within said envelope, eaeh of said electrodes having a meta1 surface portion which absorbs a halogen, an ionizab1e gaseous mgdiurn within said envelope containing a halogen gas, and a coating comprising chromium sesquioxide over a major portion of the metal surfaces of said electrodes.

2. A radiation neunter tube comprising an envelope, a pair of electrodes within said envelope, each of said electrodes having a meta1 surface portion which abs'orbs a halogen, an ionizable gaseous medium Within said envelope containing chlorine, and a coating comprising chromiurn sesquioxide over a major portion of the metal surfaces of said electrodes.

3. A radiation munter tube comprising an envelope, a pair of electrodes within said envelope, the larger cf said electrodes being constituted by an alloy of chromium and iron, an ionizable gaseous' mediurn Within said envelope containing a halogen gas, and a co ating of chromium sesquioxide over the surface of said 1arger e1ectrode.

4. A radiation counter tube comprising an envelope, a mica window in said envelope, a pair cf electrodes within said envelope, .each of saidelectrodes being co-nstituted by an a1loy of chromium and iron, an ionizable gaseous medium within said envelope containing chlorine, and a coating of chrornium sesquioxide over a major portion of the surfaces of said electrodes.

5. A radiation counter tube cornprising an envelope, a mica winglow pow der-gla ss sealed in said envelope, a pair of electrodes one of which constitutes a Wall of said envelope, said one electrode being const'ituted by an alloy of chromium and iron, an ionizable gaseous' medium Whin said envelope containing chlorine, and a coating of chromium sesquioxide over the entire surface of said one electrode.

6. A radiation counter tube comprising an envelope, a pair 0f electrodes within said enve1ope one of said e1ectrodes being substaptially larger than the other and having a metal snrface portion which absorbs a halogen, an ionizable gasepps mediurn Within said envelope containing a halogen, and a coating comprising chromium sesquioxide over the surface of said1arger electrod'e.

References Cited in the file of this patent UNITED STATES PATENTS 

1. A RADIATION CONTENT TUBE COMPRISING AN EVELOPE, A PAIR OF ELECTRODEW WITHIN SAID ENVELOPE, EACH OF AID ELECTRODES HAVING A METAL SURFACE PORTION WHICH ABSORBS A HALOGEN, AN INOIZABLE GASEOUS MEDIUM WITHIN SAID ENVELOPE CONTAINING A HOLOGEN GAS, AND A COATING COMPRIS- 